Re: [PATCH v6 1/9] drm/i915/dpcd_bl: Remove redundant AUX backlight frequency calculations

[Jani Nikula]

On Fri, 21 May 2021, Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx> wrote:
> On Fri, May 14, 2021 at 02:14:55PM -0400, Lyude Paul wrote:
>> Noticed this while moving all of the VESA backlight code in i915 over to
>> DRM helpers: it would appear that we calculate the frequency value we want
>> to write to DP_EDP_BACKLIGHT_FREQ_SET twice even though this value never
>> actually changes during runtime. So, let's simplify things by just caching
>> this value in intel_panel.backlight, and re-writing it as-needed.
>> 
>> Changes since v1:
>> * Wrap panel->backlight.edp.vesa.pwm_freq_pre_divider in
>>   DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP check - Jani
>
> This looks okay to me now... Jani, agree?

Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>


>
>> 
>> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
>> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
>> Cc: Dave Airlie <airlied@xxxxxxxxx>
>> Cc: greg.depoire@xxxxxxxxx
>> ---
>>  .../drm/i915/display/intel_display_types.h    |  1 +
>>  .../drm/i915/display/intel_dp_aux_backlight.c | 65 ++++++-------------
>>  2 files changed, 20 insertions(+), 46 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
>> index 9c0adfc60c6f..7054a37363fb 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
>> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
>> @@ -311,6 +311,7 @@ struct intel_panel {
>>  		union {
>>  			struct {
>>  				u8 pwmgen_bit_count;
>> +				u8 pwm_freq_pre_divider;
>>  			} vesa;
>>  			struct {
>>  				bool sdr_uses_aux;
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
>> index 8e9ac9ba1d38..68bfe50ada59 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
>> @@ -373,50 +373,6 @@ intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state,
>>  	}
>>  }
>>  
>> -/*
>> - * Set PWM Frequency divider to match desired frequency in vbt.
>> - * The PWM Frequency is calculated as 27Mhz / (F x P).
>> - * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
>> - *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
>> - * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
>> - *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
>> - */
>> -static bool intel_dp_aux_vesa_set_pwm_freq(struct intel_connector *connector)
>> -{
>> -	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
>> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
>> -	const u8 pn = connector->panel.backlight.edp.vesa.pwmgen_bit_count;
>> -	int freq, fxp, f, fxp_actual, fxp_min, fxp_max;
>> -
>> -	freq = dev_priv->vbt.backlight.pwm_freq_hz;
>> -	if (!freq) {
>> -		drm_dbg_kms(&dev_priv->drm,
>> -			    "Use panel default backlight frequency\n");
>> -		return false;
>> -	}
>> -
>> -	fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
>> -	f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
>> -	fxp_actual = f << pn;
>> -
>> -	/* Ensure frequency is within 25% of desired value */
>> -	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
>> -	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
>> -
>> -	if (fxp_min > fxp_actual || fxp_actual > fxp_max) {
>> -		drm_dbg_kms(&dev_priv->drm, "Actual frequency out of range\n");
>> -		return false;
>> -	}
>> -
>> -	if (drm_dp_dpcd_writeb(&intel_dp->aux,
>> -			       DP_EDP_BACKLIGHT_FREQ_SET, (u8) f) < 0) {
>> -		drm_dbg_kms(&dev_priv->drm,
>> -			    "Failed to write aux backlight freq\n");
>> -		return false;
>> -	}
>> -	return true;
>> -}
>> -
>>  static void
>>  intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
>>  				   const struct drm_connector_state *conn_state, u32 level)
>> @@ -459,9 +415,13 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
>>  		break;
>>  	}
>>  
>> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
>> -		if (intel_dp_aux_vesa_set_pwm_freq(connector))
>> +	if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
>> +		if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
>> +				       panel->backlight.edp.vesa.pwm_freq_pre_divider) == 1)
>>  			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
>> +		else
>> +			drm_dbg_kms(&i915->drm, "Failed to write aux backlight frequency\n");
>> +	}
>>  
>>  	if (new_dpcd_buf != dpcd_buf) {
>>  		if (drm_dp_dpcd_writeb(&intel_dp->aux,
>> @@ -482,6 +442,14 @@ static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state
>>  				  false);
>>  }
>>  
>> +/*
>> + * Compute PWM frequency divider value based off the frequency provided to us by the vbt.
>> + * The PWM Frequency is calculated as 27Mhz / (F x P).
>> + * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
>> + *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
>> + * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
>> + *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
>> + */
>>  static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connector)
>>  {
>>  	struct drm_i915_private *i915 = to_i915(connector->base.dev);
>> @@ -533,8 +501,10 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
>>  	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
>>  	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
>>  
>> +	/* Ensure frequency is within 25% of desired value */
>>  	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
>>  	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
>> +
>>  	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
>>  		drm_dbg_kms(&i915->drm,
>>  			    "VBT defined backlight frequency out of range\n");
>> @@ -555,7 +525,10 @@ static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connecto
>>  			    "Failed to write aux pwmgen bit count\n");
>>  		return max_backlight;
>>  	}
>> +
>>  	panel->backlight.edp.vesa.pwmgen_bit_count = pn;
>> +	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
>> +		panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
>>  
>>  	max_backlight = (1 << pn) - 1;
>>  
>> -- 
>> 2.31.1
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center